'Digital fingernail' could control digital devices

By Laura Onita

Published Friday, April 17, 2015

Researchers have developed a new wearable device that turns the user’s thumbnail into a miniature wireless track pad.

The wearable sensor, called NailO, could let users control wireless devices when their hands are full such as answering the phone while cooking and could also improve other device interfaces, allowing someone texting on a smartphone to switch between symbol sets without interrupting their typing, for instance.

The prototype is the brainchild of Cindy Hsin-Liu Kao, an MIT graduate and lead author on the paper, and was inspired by nail stickers. “It’s very unobtrusive,” Kao said. “When I put this [sensor] on, it becomes part of my body. I have the power to take it off, so it still gives you control over it. But it allows this very close connection to your body.”

The researchers used capacitive sensing – the same as the one the iPhone’s touch screen relies on – to register touch and the device can tolerate a thin, non-active layer between the user’s finger and the underlying sensors.

The device features capacitive sensors, a battery and three separate chips – a microcontroller, a Bluetooth radio chip, and a capacitive-sensing chip – all packed into a space no larger than a thumbnail.

“The hardest part was probably the antenna design,” said Artem Dementyev, the paper’s other lead author. “You have to put the antenna far enough away from the chips so that it doesn’t interfere with them.”

For their initial prototype, the researchers built their sensors by printing copper electrodes on sheets of flexible polyester. Although it allowed them to experiment with a range of different electrode layouts, in ongoing experiments they are using off-the-shelf sheets of electrodes such as those found in some track pads.

At such small scales, however, energy efficiency is at a premium, so the device would have to be deactivated when not actually in use.

Talking about wearable technology and the device that might well be a ‘digital fingernail’, Steve Hodges, sensors and devices researcher at Microsoft Research in Cambridge, said: “NailO is interesting because it’s thinking about much more subtle interactions, where gestures or speech input are socially awkward.”